Petroleum-related geomaterials are complex materials that are formed by the accumulation of sediments (minerals and fragments from other rocks), are compacted and partially cemented over time, and may be subjected to localized or widespread digenetic alterations that transform their texture and overall composition to their final form. In general, these materials include detrital grains, rock fragments, and a large variety of matrix forming minerals, which may be arranged in various ways, depending on their shapes and size distributions, and in the manner by which they were deposited and altered after deposition. Geomaterials also contain voids (that may be connected or isolated) and pore fluids (water, liquid hydrocarbons or gas). Thus, geomaterials' bulk properties result from their composition and the textural arrangement of their constituents, and include shapes and orientations of pore spaces. As the source of detrital, the conditions of deposition and the post-depositional digenetic alteration changes with time (gradually or abruptly), and the sedimentary column is built up by a sequence of layers whose boundaries may be sharp or transitional, whose properties may be similar or strongly different to each other. As a result, lithologic units are often interbedded with multiple lithofacies, some of which may be further altered diagenetically, or by interaction with living organisms. Geomaterials are thus heterogeneous at many scales (from micro-textural scale to basin scale), and their properties vary vertically and laterally at many scales.